AWS Network Limits and Limitations

It is good to know about the AWS network limits both for planning and troubleshooting: you can build your architecture to allow you to overcome these limits and it saves you time of troubleshooting when there is a failure or downtime in your network.

For example, an AWS VGW carries a hard limit of 100 BGP routes in total. When the BGP prefixes exceed 100, VGW randomly resets the BGP session, leading to unpredictable potential network downtime.

AWS publishes VPC limits at this link.

In addition to limits, there are limitations in functionality.

Below is a list of commonly asked limits and limitations by network engineers.

Functions	Limits	Comments
VPC Peering Limit per VPC	125	default limit is 50. Constrained also by route limit of 100
VPC Route entries in a route table	100	default is 50. Performance impact on 100 routes.
BGP prefix total on VGW	100	exceeding the limit results in random BGP resets
VGW instance size scaling	reset BGP	trigger a BGP downtime
DNAT function in VGW	not available
SNAT function in VGW	not available
NAT Gateway policies	not available
VPN connections per VPC	10
VPN traffic initiation	from on-prem	traffic must be initiated from on-prem to establish a VPN tunnel with VGW
VIF per Direct Connect	50
Inter region peering MTU size	1500 bytes	unlike intra region peering, there is no jumbo frame support, therefore inter region performance is maxed out at 5Gbps.
Outgoing SMTP traffic on port 25	throttled	you can send a request to lift the throttle.